Radiation-sensitive compositions are routinely used in the preparation of imageable materials including lithographic printing plate precursors. Such compositions generally include a radiation-sensitive component, an initiator system, and a binder, each of which has been the focus of research to provide various improvements in physical properties, imaging performance, and image characteristics.
Recent developments in the field of printing plate precursors concern the use of radiation-sensitive compositions that can be imaged using lasers or laser diodes, and more particularly, that can be imaged or developed on-press. Laser exposure does not require conventional silver halide graphic arts films as intermediate information carriers (or “masks”) since the lasers can be controlled directly by computers. High-performance lasers or laser-diodes that are used in commercially-available image-setters generally emit radiation having a wavelength of at least 700 nm, and thus the radiation-sensitive compositions are required to be sensitive in the near-infrared or infrared region of the electromagnetic spectrum. However, other useful radiation-sensitive compositions are designed for imaging with ultraviolet or visible radiation.
There are two possible ways of using radiation-sensitive compositions for the preparation of printing plates. For negative-working printing plates, exposed regions in the radiation-sensitive compositions are hardened and unexposed regions are washed off during development. For positive-working printing plates, the exposed regions are dissolved in a developer and the unexposed regions become an image.
Imaged elements are often baked after development to increase their on-press run length. U.S. Patent Application Publication 2009/0042135 (Patel et al.) describes positive-working multilayer imageable elements that contain specific polymers having acidic groups dispersed within the inner layer to improve post-development bakeability and chemical solvent resistance. Other imageable elements with improved resistance to press chemicals and bakeability are described for example in U.S. Pat. No. 7,049,045 (Kitson et al.), U.S. Pat. No. 7,144,661 (Ray et al.), U.S. Pat. No. 7,186,482 (Kitson et al.), and U.S. Pat. No. 7,247,418 (Saraiya et al.
U.S. Patent Application Publication 2009/0142695 (Baumann et al.) describes imageable elements that contain non-polymeric or polymeric components having 1H-tetrazole groups that provide improved chemical resistance and on-press printing run length.
While known imageable elements demonstrate excellent imaging and printing properties, there is a need to further improve the post-development bakeability or to reduce baking temperature and time while maintaining other desired properties including resistance to press chemicals. It is also desirable to reduce the baking temperature and time while maintaining on-press run length.